MaxHopCount
Set maximum hop count All versions
A hop is the transmittal of a
mail message from one machine to another.[394] Many hops might be required to deliver a
message. The number of hops is determined by
counting the Received:, Via:, X400-Received, and Mail-From: lines in the
header of an email message.[395]
The MaxHopCount
option tells sendmail the
maximum number of times a message can be forwarded.
When sendmail receives a
message via email, it calculates the hop count. If
that count is above the maximum allowed, it bounces
the message back to the sender with the
error:
sendmail: too many hops (17 max)
In this case, 17 is
the maximum. Detecting too many hops is useful in
stopping mail loops—messages
being forwarded back and forth between two
machines.
The forms of the MaxHopCount option are as
follows:
O MaxHopCount=hops ← configuration file (V8.7 and later) -OMaxHopCount=hops ← command line (V8.7 and later) define(`confMAX_HOP',hops) ← mc configuration (V8.7 and later) Ohhops ← configuration file (deprecated) -ohhops ← command line (deprecated)
The hops argument is of
type numeric. If
hops is missing, the
value becomes zero and causes all mail to fail with
the error:
sendmail: too many hops (0 max)
If the entire MaxHopCount option is missing,
hops defaults to 25. A
good value is 50 or more (RFC2821, Command-Line Switches, suggests 100). This allows mail to follow a fairly long route through many machines (as it could with UUCP) but still catches and bounces mail caught in a loop ...
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